The decay of unstable atoms is often accompanied by the energetic emission of ionizing radiation in the form of particles or electromagnetic waves. These emissions may take various forms such as alpha particles, beta particles (electrons), gamma rays (photons), neutrons, and positrons. Due to their very short range in human tissue, the energy from this radiation is largely absorbed by the tissue and can result in very high radiation doses. The dose can be especially large in the case where a radioactive material (e.g., a “hot particle”) is in contact with the skin. Since tissue is prone to adverse biological responses to the absorption of this nuclear energy, it is quite important to estimate the hot-particle dose, i.e., the amount of energy per unit mass (of tissue), given that a person was or may have been exposed to a hot particle on their skin or on the clothing above their skin.
Such dose estimates are needed for workers in the nuclear power industry. Radiopharmaceutical companies and hospitals may also employ the use of radiation-emitting nuclides in their operations. These nuclides could be in a solid physical form, in which case they may behave like hot particles, or they may exist in liquid form. As liquids, skin contamination could occur if the liquid were spilled or otherwise came into contact with the skin or clothing. Whether solid or liquid, exposure to tissue by these hot particles or liquid radio-nuclides would result in the necessity to perform a dose assessment following the skin contamination event. In addition to these biological reasons, the U.S. Nuclear Regulatory Commission requires a licensee to document radiation exposures, and they are quite specific regarding exposures to the skin.
A wide variety of devices and techniques have evolved to assist in dose assessment. Commonly known techniques are based on the use of a thermoluminescent dosimeter (TLD) to register radiation dose to skin layers and deep tissue. These passive devices are typically worn by workers and use TLD phosphors to record accumulated radiation energy deposition information. At a later time and location, the integrated radiation dose to the TLD phosphors is measured and translated to estimates of shallow and deep dose in tissue. These passive techniques, however, do not provide real-time, on-site assessment or dosimetry.
Computer models such as the widely used VARSKIN computer code can be used to calculate skin dose from data representing the radioactive contamination. These computational models, however, do not measure dose directly from actual measurements of radiation. Also, using these computational models, skin dosimetry as a function of depth following contamination occurs at a later time and place after much preparation and characterization of the radiation source.
Some known skin dosimetry devices use a scintillator to measure a counting rate of a single type of radiation at a specific energy and estimate a corresponding dose in skin tissue. Although such devices provide real-time information, they are limited to a small energy range of a single type of radiation and fail to provide an estimate of the dose due to other types of radiation. Nor do they provide estimates of dose at various skin depths.
Scintillation detectors have been used for many years in various applications for the general purpose measurement of different types of radiation including alpha, beta, gamma and neutron energy deposition. Of particular significance are the devices and techniques for simultaneous beta and gamma spectroscopy that were developed by two of the present inventors and described in U.S. Pat. No. 7,683,334, which is incorporated herein by reference. This earlier work, however, did not provide any device or technique for skin dosimetry.